1. Technical Field
The present invention relates to a calibration apparatus for an image forming apparatus, a non-transitory computer readable storage medium stored with program for the calibration apparatus, and a method for calibrating the image forming apparatus.
2. Description of Related Art
An entire color reproducibility accuracy evaluation in an image forming apparatus typically employs a color matching evaluation using a color difference ΔE as index. However, only the color matching using the color difference ΔE is insufficient for calibrating the image forming apparatus, and a gray balance color reproducibility accuracy (which will be called “gray balance accuracy” below) needs to be enhanced in addition to the entire color reproducibility accuracy.
On the other hand, by a feedback to a gray balance of a colorimetric value repeatedly in calibration, enhancement of a gray balance accuracy would be achieved, but even if the feedback is further repeated toward the limit of the improvement in gray balance accuracy, the gray balance accuracy lasts at the same level. Thus, other indexes for color reproducibility need to be considered in order to determine which of the gray balances obtained by multiple feedbacks is optimum.
As to a technique for calibrating an image forming apparatus, as disclosed in Unexamined Japanese Patent Publication No. 2003-14544, there are displayed a plurality of evaluation scales such as color difference obtained by a colorimetric value of a reference image and a colorimetric value of an image to be evaluated, metric value, color reproducibility indexes and color difference statistics calculated therefrom. Thereby, an accurate evaluation for total color reproducibility is enabled.
However, there is a problem that the above conventional technique is complicated because of many factors to be determined for comparing and determining multiple feedback results.
Further, if a red-stronger color deviation and a blue-stronger color deviation for a color to be originally expressed are mixed in an image, a color reproducibility with visual evaluation is worse on an actual printed material than a deviation of a color difference ΔE obtained by the numerical evaluation. However, the above conventional technique has a problem that optimum calibration is not executed in terms of inversion of the color deviation direction.